A crucible or a jig to be used for manufacturing single crystal for the use of a semiconductor has heretofore been manufactured by using a quartz powder obtained by pulverizing natural quartz or silica sand and purifying the same as a raw material. However, the natural quartz or the silica sand contains various metal impurities, and even when the above purification treatment has been done, the metal impurities cannot completely be removed, so that it cannot be sufficiently satisfied in the point of purity. Also, accompanied by the progress of high integration of the semiconductor, a quality of the single crystal which becomes a material has been required to be heightened, whereby the crucible or the jig used for manufacturing the single crystal has also been required to be a high purity product. Therefore, a synthetic silica glass product using a high purity synthetic amorphous silica powder as a raw material has been attracted attention in place of the natural quartz or the silica sand.
As a process for manufacturing the high purity synthetic amorphous silica powder, a method in which high purity silicon tetrachloride is hydrolyzed by water, and the formed silica gel is dried, sized and fired to obtain a synthetic amorphous silica powder has been disclosed (for example, see Patent Document 1). It has also been disclosed a method in which an alkoxysilane such as a silicic acid ester is hydrolyzed in the presence of an acid and an alkali to make a gel, and the obtained gel is dried, pulverized and fired to obtain a synthetic amorphous silica powder (for example, see Patent Documents 2 and 3). Further, it has been disclosed a method in which a slurry of fumed silica is produced, and it is dried, pulverized and then calcined to obtain a synthetic amorphous silica powder (for example, see Patent Documents 4 and 5). The synthetic amorphous silica powders manufactured by the methods described in the above-mentioned Patent Documents 1 to 5 have high purity as compared with the natural quartz or the silica sand, so that it is possible to reduce migration of impurities from the synthetic silica glass product such as a crucible or a jig manufactured by using these as raw materials or to make the product high performances.